I haven't heard of compatible numbers but rational numbers, here you go: http://www.mathsisfun.com/rational-numbers.html
Just click the link or you can right click it and open in new tab.
Ok, this one is extremely crazy! As the peon says, "Work, work!"
You need to do a couple of big expansions...use this: http://www.wolframalpha.com/widget/widgetPopup.jsp?p=v&id=6767c31553b5f2c292b426c97a9b6013&title=Binomial+Expansion+Calculator&theme=blue&i0=a%2B2b%2B3x&i1=6&podSelect&includepodid=Input&includepodid=